1. Field of the Invention
The present invention relates to a base station apparatus and method of deciding a master base station apparatus.
2. Description of the Related Art
In a related art communication system (for example, a PBX (Private Branch eXchange) wireless system), a communication terminal sequentially switches a base station targeted for communication among plural base station apparatuses (hereinafter also called a “base station” simply) to move. Such switching between the base stations is called a handover. The plural base stations must synchronize timing of transmitting and receiving mutually in order that the communication terminal communicating with the base station using a time division wireless communication scheme (for example, TDMA/TDD) suitably hands over between the plural base stations.
As methods for synchronizing the plural base stations, the following methods are known. A time information server transmits time information to the plural base stations through a LAN (Local Area Network). Then, each of the base stations adjusts a clock generator of the inside of its own apparatus based on the time information and a point in time of receiving the time information (for example, see JP-T-2003-509973).
Also, the following method is known. Among plural base stations, a master-slave relation (synchronous tree) is built as a master for generating transmission timing and reception timing and a slave for synchronizing with its master, and one base station is set as the master with the highest layer. The other base stations operate as the slaves for following the base stations with the high layers, and receive a synchronous signal transmitted from the master base station by wireless, and sets its own transmission timing and reception timing. Then, the slave base station corrects a lag in the transmission timing and the reception timing with respect to the other side of synchronization at predetermined time intervals (for example, see JP-A-2002-165269).
Also, the following method is known. JP-A-2006-50636 discloses that an ad hoc network is organized from a set of plural nodes and a central coordinator node is automatically selected. This is the method in which a topology map for describing quality and the number of communication links between the nodes with respect to all the nodes is created and the best candidate node is selected from this map information and an efficient network capable of a high-definition two-way communication link between the nodes is achieved (see JP-A-2006-50636).